Induction motors are widely used in home appliances and other electromechanical systems. Induction motors typically produce torque to drive a load by applying a current to one or more stator windings to create a magnetic field. The magnetic field of the stator windings induces a current in a rotor, which in turn creates magnetic fields in the rotor that react against the magnetic field of the stator windings, and causes the rotor to rotate.
In conventional single speed induction motors, such as permanent split capacitor (PSC) motors, the motor is driven by turning on an alternating current switching element, such as a Triac, to allow current to be applied to the motor. Variable speed operation is often desirable and may be achieved by skipping AC cycles or phase controlling the Triac. Phase controlling generally produces better performance in terms of speed regulation and audible noise. However, the inductive properties of the induction motor cause the motor current to lag the voltage, which can cause inefficient operation of the induction motor at low phase delays (higher power). In particular, as the Triac is a current controlled device, such lagging current can cause failed Triac gating at low phase delays, which can lead to significantly reduced performance of the motor.